For graham crust, in a large microwave-safe bowl, microwave 6 tablespoons of the butter on high about 1 minute or until melted. Add graham cracker crumbs and the 3 tablespoons sugar, stirring with a fork until mixture comes together. Press into the bottom of the prepared baking pan.

Bake graham crust for 15 minutes. Cool in pan on a wire rack.

Meanwhile, in a large saucepan, combine the remaining 6 tablespoons butter, the remaining 2 cups sugar, and the evaporated milk. Cook and stir over medium heat until boiling; boil for 10 minutes, stirring occasionally.

Remove from heat. Add 3 cups of the marshmallows and 3 cups of the miniature chocolate bars, stirring until smooth. Cool at room temperature for 15 minutes.

Sprinkle the remaining 1 cup marshmallows over the cooled graham crust. Pour the cooked mixture over the marshmallows in baking pan. Press the remaining 1/4 cup miniature chocolate bars into the top of the fudge, spacing bars evenly. Cool at room temperature for 1 hour. Chill in refrigerator about 2 hours or until set.